Certain industries, such as the airline and banking industries, require their data processing systems to be up and running twenty-four hours a day. They cannot afford to have their systems unavailable for any amount of time, no matter how small that amount of time may be. Thus, efforts are continually being made to increase system availability.
In one example, system availability is enhanced by enabling operating system software to be modified while the system is running. One technique for dynamically modifying system software is described in U.S. Pat. No. 5,359,730 entitled "Method of Operating a Data Processing System Having A Dynamic Software Update Facility," issued on Oct. 25, 1994 and assigned to International Business Machines Corporation.
In particular, the patent discloses a technique for non-disruptively replacing old operating system programs with new updated versions while providing continuous availability and operation of the data processing system. Specifically, new versions of the software are loaded into the system along with change instructions providing information controlling the update. Initially, every invocation of the old version is intercepted by the system, and the dynamic software update facility determines the state of the process which invoked the program. If the process is "unsafe", the facility passes control to the old version of the program. However, if the process is "safe", then control is passed to the new version.
The above-described technique however, does not address the problem of migrating shared data from an old format to a new format without disrupting system availability. For instance, assume that a data processing system includes two processors, each of which shares a datum stored on an external storage media. Typically, in order to reformat that datum, the data processing system is brought down, the datum is reformatted, new programming code is loaded onto each of the processors to use the reformatted datum, and the processors are brought back up. This necessarily disrupts system availability causing serious problems for high or continuous availability systems.
Based on the foregoing, a need exists for a data conversion technique, which is non-disruptive to the availability of the data processing system. Further, a need exists for a technique that allows one processor to use the data in one format, while another processor uses the data in another format. A further need exists for a data conversion technique that is dynamic and transparent to the user in that the user does not have to be aware of the structure of a particular datum. A yet further need exists for a technique that does not require the storing, maintaining and synchronizing of the data in the new and old formats. A further need exists for a technique that permits the reformatted datum to be backed out to its previous format without disruption to the data processing system.